Bounce e-mail

A bounce e-mail always occurs when an accepted e-mail is rejected due to any error. This serves to inform the sender of the original e-mail about the problem.

Misdirected bounce e-mail

A bounce e-mail is misdirected if the sender address was faked and the returned bounce e-mail therefore reaches a sender who did not send the original e-mail.
This means that the wrong person is informed of an error that was not caused by them.

MX / MX record

MX is short for mail exchanger, after the entry in the DNS (Domain Name Server). This entry specifies the mail server responsible for the domain.
For example, the command nslookup -q=mx rz.rwth-aachen.de can be used to query the mail domain of the IT Center of RWTH Aachen University.